On Dec 11, 2013, at 10:34 AM, Markus Lanthaler <markus.lanthaler@gmx.net> wrote:
> On Wednesday, December 11, 2013 7:18 AM, Thomas Baker wrote:
>> On Tue, Dec 10, 2013 at 11:29:00PM -0600, Pat Hayes wrote:
>>>> Works for me. We could perhaps make it even simpler by just saying
>>>>
>>>> A relationship that holds between two resources at one time may
>>>> not hold at another time.
>>
>> Pat's answer (below) is certainly the more interesting. However, the
>> simple bulleted list at [1] is not a good place to first raise such a
>> subtle issue. If Pat's judgement amounts to weak assent, I'd vote +0.5
>> for the "least bad" variant above.
>
> OK, I went ahead and made the change. Tom, Pat, could you please tell me
> whether you can live with this so that we can close ISSUE-178?
Yes, I can live with it.
Pat
>
>
> Thanks,
> Markus
>
>
>
>> [1] https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-
>> concepts/index.html#change-over-time
>>
>>> This last one is the least bad of the lot. But none of them are
>> correct.
>>> There is a basic issue here. Just like sets, relations cannot really
>> change
>>> with time. At least, not when they are described using a normal logic
>> (they
>>> can in a tense logic). What can happen is that something that we
>> might
>>> casually or carelessly describe as a binary relation is in fact a
>> three-way
>>> relation with time as its third argument. Now of course [ R(a, b) at
>> T ] or
>>> R(a, b, T) pretty much mean the same thing and in English we don't
>> even have
>>> a way to distinguish them; but being all logical and strict about it,
>> the
>>> three-argument way of talking is more accurate precisely because it
>> makes it
>>> clear that the *actual relation* does not change, which makes sense
>> because
>>> relations (speaking now formally and mathematically proper), like
>> sets, just
>>> aren't the kind of thing that can possibly change. (If this reminds
>> y'all of
>>> the problems we had with talking about RDF graphs being updated or
>> modified,
>>> yes it is exactly the same issue.) We could have made RDF into a
>> tensed
>>> logic, in which all assertions are made at a time, and things like a
>> triple
>>> being true AT a time would make literal sense; but we didn't. So
>> right now,
>>> and probably for the forseeable future, the idea of a relation
>> changing -
>>> holding at one time but not at another time - does not make sense
>> according
>>> to the RDF conceptual model, so temporal variation like this has to
>> be
>>> modeled in the same way we would model a three-place relation in RDF.
>>>
>>> We might say something like this:
>>>
>>> Some relations have an extra time parameter or are time-dependent.
>> Such a
>>> relationship that holds between two resources at one time might not
>> hold at
>>> another time. To describe this in RDF we have to treat the time as an
>> extra
>>> argument or parameter to the binary relation.
>>
>> --
>> Tom Baker <tom@tombaker.org>
>
>
> --
> Markus Lanthaler
> @markuslanthaler
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